1. Field of the Invention
The present invention relates to a rotational angle detector, and particularly to a rotational angle detector which prevents a controlled system from being improperly controlled by promptly identifying an abnormality of a detected angle detection signal or by promptly outputting an angle set signal with an abnormality signal added, when the rotational state of a rotor such as the steering shaft of a vehicle is detected as an angle detection signal, an angle set signal is generated based on the result of the detection and the controlled system is controlled using the angle set signal.
2. Description of the Related Art
Generally a rotational angle detector is designed to detect the rotational angle of a rotor to control a controlled system according to the result of the detection. It comprises at least the following: a rotational angle detecting section which detects the rotational state of the rotor, generates an angle detection signal and sends the angle detection signal to a control section; a control section which generates an angle set signal by performing calculation on the received angle detection signal in a prescribed manner and sends the angle set signal to a bus line; and a controller which receives the angle set signal sent through the bus line and controls the controlled system in response to the received angle set signal.
When this rotational angle detector is to be used to detect the rotational angle of the steering shaft of a vehicle, the detector is mounted in the vehicle with its rotational angle detection section connected to the steering shaft of the vehicle.
Various types of rotary sensors are available for use in the rotational angle detecting section of a rotational angle detector mounted in a vehicle. One such rotary sensor will be described next.
FIG. 10A and FIG. 10B are sectional views showing an example of the structure of one of the above-said rotary sensors; FIG. 10A is a transverse sectional view and FIG. 10B is a sectional view taken along the line 10Bxe2x80x9410B of FIG. 10A.
As illustrated in FIG. 10A and FIG. 10B, this rotary sensor comprises: a case 71, a rotor 72, a rotary shaft 73, a bearing 74, a worm gear 75, a slider 76, a first magnet 771, a second magnet 772, a first Hall element 781, a second Hall element 782, a third Hall element 783, and a circuit board 79. In this case, the rotor 72 is connected with the steering shaft of the vehicle at its center and there are many gear teeth on its circumference. The rotary shaft 73, around which the worm gear 75 is fitted, rotates in conjunction with the worm gear 75. The screw grooves in the outer surface of the rotary shaft 73 engage with the screw grooves in the inner surface of the slider 76 so that the slider 76 slides in the axial direction of the rotary shaft 73 as the rotary shaft 73 turns. When the worm gear 75 and the gear teeth of the rotor 72 engage with each other and the rotor 72 turns, the rotary shaft 73 also turns by the mediation of the worm gear 75 at a prescribed rotation ratio with respect to the rotor 72. The worm gear 75 has a cylindrical magnet holder 75A at one end of it and the cylindrical first magnet 771 is fitted on the circumference of the magnet holder 75A. The slider 76 has a planar second magnet 772 attached on its outer surface. Attached on the circuit board 79, which is arranged in parallel to the rotary shaft 73, are the first Hall element 781, the second Hall element 782 and the third Hall element 783. The first Hall element 781 and the second Hall element 782 are located adjacent to the outer surface of the first magnet 771, forming an angle of approximately 90 degrees with respect to the central axis of the first magnet 771. The third Hall element 783 is located adjacent to the outer surface of the second magnet 772.
As the rotor 72 turns, a sinusoidal waveform first angle detection signal and a sinusoidal waveform second angle detection signal are issued with a quarter-wave phase difference from the first Hall element 781 and the second Hall element 782 respectively, with a constant maximum amplitude and the same cycle. At the same time, the third Hall element 783 issues a third angle detection signal which increases linearly with the full rotation range of the rotor 72 constituting one cycle.
The first angle detection signal, second angle detection signal and third angle detection signal from the rotary sensor are sent to the control section. The control section roughly determines the rotational angle and direction with respect to the neutral position of the steering wheel (steering shaft) according to the received third angle detection signal and finely determines the rotation angle with respect to the neutral position of the steering wheel according to the received first and second angle detection signals. The control section generates an angle set signal based on the result of detection of the rotational angle and direction with respect to the neutral position of the steering wheel, and sends the generated angle set signal through the bus line to the controller. According to the angle set signal it has received, the controller accurately controls a controlled system such as the suspension system or traction control system of the vehicle.
FIG. 8 is a characteristic graph showing the relation between the steering wheel rotational angle and the voltage of each of the first to third angle detection signals, which are all sent from the rotary sensor, in a rotational angle detector based on the above-said rotary sensor.
In FIG. 8, reference numeral 51 represents the first angle detection signal, 52 the second angle detection signal and 53 the third angle detection signal; this graph shows changes in the voltage of each of the first to third angle detection signals 51, 52, 53 in the whole range of steering wheel rotation (xc2x1720 degrees from the neutral position).
Here, the first angle detection signal 51 and the second angle detection signal 52 are sinusoidal waveform signals with the same maximum amplitude and the same cycle, between which there is a quarter-wave phase difference, where they both have a maximum voltage of 4.5 V and a minimum voltage of 0.5 V. For the first angle detection signal 51, the voltage is the minimum (0.5 V) at a rotational angle of xe2x88x9222.5 degrees from the neutral position (0 degree) and rotational angles decreasing from xe2x88x9222.5 degrees in decrements of xe2x88x9290 degrees, and at a rotational angle of +67.5 degrees and rotational angles from +67.5 degrees in increments of +90 degrees. For the second angle detection signal 52, the voltage is the minimum (0.5 V) at a rotational angle of 0 degree (neutral position) and rotational angles decreasing from 0 degree in decrements of xe2x88x9290 degrees and rotational angles increasing from 0 degree in increments of +90 degrees. For the third angle detection signal 53, the voltage linearly increases over the rotational angle range from xe2x88x92720 degrees to +720 degrees, with the minimum voltage (0.5 V) at xe2x88x92720 degrees of rotational angle and the maximum voltage (4.5 V) at +720 degrees of rotational angle.
FIG. 9 is a fragmentary view of the characteristic graph in FIG. 8 where the part ranging from xe2x88x9290 degrees to +90 degrees is enlarged.
In FIG. 9, 51U represents a virtually linear leading edge (gradient) for the first angle detection signal 51, 51D a virtually linear trailing edge (gradient) for the first angle detection signal 51, 52U a virtually linear leading edge (gradient) for the second angle detection signal 52, and 52D a virtually linear trailing edge (gradient) for the second angle detection signal 52. The same other elements as those shown in FIG. 8 are designated with the same reference numerals.
Next, how the rotational direction and angle of the steering wheel are detected by the control section will be explained referring to the characteristic graphs shown in FIG. 8 and FIG. 9.
First, the control section detects the rotational direction from the neutral position (rotational angle of 0 degree) of the steering wheel according to the voltage of the third detection signal it has received. Concretely, if the voltage of the third detection signal 53 is over 2.5 V, it detects that the steering wheel has been turned in one direction (positive angle), while if the voltage of the third detection signal 53 is below 2.5 V, it detects that the steering wheel has been turned in the other direction (negative angle).
Next, the control section roughly determines a rotational angle as follows. As illustrated in FIG. 9, the whole rotational angle range of the steering wheel (for example, 1440 degrees, or xc2x1720 degrees) is divided into segments named Nxe2x88x921, N, N+1 and so on with one segment (for example, 90 degrees) corresponding to one wavelength of the first angle detection signal 51 and second angle detection signal 52. The control section detects in which of the angle segments Nxe2x88x921, N, N+1 the voltage of the received third angle detection signal 53 falls, in order to determine a rough rotational angle. For instance, if the voltage of the third angle detection signal 53 is found to be 2.8 V, the control section determines that it is the angle segment N that corresponds to that voltage.
Then, from the angle segment N, the control section obtains the first voltage value V1 and second voltage value V2, or points where the voltage of the received first angle detection signal 51 coincides with that of the second angle detection signal 52. Referring to the first voltage value V1 and second voltage value V2 thus obtained, the control section identifies either of the angle detection signals as a signal out of the V1-V2 range and the other signal as a signal within the V1-V2 range, in each sub-segment of the segment N.
Then, the control section decides whether the other angle detection signal within the V1-V2 range is either the first angle detection signal 51 or the second angle detection signal 52. At the same time, the control section decides whether the one angle detection signal out of the V1-V2 range is either smaller than the first voltage value V1 or larger than the second voltage value V2. Also it determines in which one of the four sub-segments (the first sub-segment H1, second sub-segment H2, third sub-segment H3 and fourth sub-segment H4) of the angle segment N the other angle detection signal, which is within the V1-V2 range, falls. In this way, the rotational angle of the steering wheel is determined more accurately by finding in which sub-segment (among the sub-segments H1 to H4 of the angle segment N) does the other angle detection signal fall.
In the example shown in FIG. 9, for the other angle detection signal which is within the V1-V2 range, the part in the first sub-segment H1 corresponds to the linear leading edge (gradient) 51U of the first angle detection signal 51; the part in the second sub-segment H2 corresponds to the linear leading edge (gradient) 52U of the second angle detection signal 52; the part in the third sub-segment H3 corresponds to the linear trailing edge (gradient) 51D of the first angle detection signal 51; and the part in the fourth sub-segment H4 corresponds to the linear trailing edge (gradient) 52D of the second angle detection signal 52.
As a consequence of the above-mentioned operational sequence, the control section finally determines the angle of the steering wheel from the first to third angle detection signals 51 to 53 it has received, and generates an angle set signal based on the determined angle.
In the known rotational angle detector as mentioned above, when a rotary sensor (rotational angle detecting section) as suggested above is employed, the rotary sensor sends the first angle detection signal 51, second angle detection signal 52 and third angle detection signal 53 to the control section as the rotor turns. When determining the rotational direction and angle according to the received first to third angle detection signals 51 to 53, the control section first detects the rotor""s rotational direction and rough rotational angle based on the amplitude (voltage) of the third angle detection signal 53, and then more accurately determines the rotor""s rotational angle based on the linear gradient of the first and second angle detection signals 51 and 52. Therefore, the control section can detect the rotor""s rotational angle and direction over a wide angle range with high accuracy and thus produce an angle set signal from the detection result with high accuracy.
However, since a rotational angle detector having the above-suggested rotary sensor (rotational angle detecting section) directly uses the first angle detection signal 51, second angle detection signal 52 and third angle detection signal 53 to detect the rotational angle and direction of the rotor, if an incorrect angle detection signal is sent from the rotary sensor for some reason, detection of rotational angle and direction detection is performed according to the incorrect angle detection signal and consequently an incorrect angle set signal is fed from the control section to the controller. If the controller has received the incorrect angle set signal, it fails to control the suspension system or traction control system of the vehicle properly; if this phenomenon continues, it will become difficult to control the vehicle properly.
The present invention has been made in view of the above technical background; the primary object of the invention is to provide a rotational angle detector which eliminates the possibility of output of an incorrect angle set signal by promptly identifying the feed of an incorrect angle set signal, or by outputting an angle set signal with an abnormality signal added upon detection of an abnormality, in order to prevent incorrect control based on an incorrect angle set signal.
In order to achieve the above object, according to one aspect of the present invention, a rotational angle detector comprises: a rotational angle detecting section which detects an angle detection signal correspondent to a rotational state of a rotor in a short cycle and feeds the angle detection signal to a control section; the control section which calculates the angle detection signal fed from the rotational angle detecting section and sends an angle set signal through a controller to a controlled system; and a memory which stores the angle detection signal temporarily and also stores an allowable maximum angle value for angle detection signals, wherein the control section has a means to make an output cycle for the angle set signal longer than a detection cycle for the angle detection signal and count a number of times when the angle detection signal as fed within the long output cycle for angle detection signals is beyond the allowable maximum angle value and, if the count is judged as being beyond a preset number, output an abnormality signal instead of the angle set signal.
In the above means, the memory stores the allowable maximum angle value for angle detection signals; and the control section counts the number of times when the angle detection signal as fed within a long output cycle for angle set signals is beyond the allowable maximum angle value and, if it decides that the count is above a preset number, outputs an abnormality signal in the next output cycle for angle set signals instead of the angle set signal. Therefore, thanks to output of the abnormality signal, the user of the rotational angle detector can not only immediately be notified of the presence of an abnormality in the operation of the rotational angle detector but also avert the risk of the controlled system being improperly controlled due to the feed of an incorrect angle set signal.
According to another aspect of the present invention, in the rotational angle detector, it is desirable that the detection cycle for angle detection signals be 400 microseconds or less and the output cycle for angle set signals be 10 milliseconds or less.
With this arrangement, when the rotational angle detector is used for the steering wheel of a vehicle, variation per detection cycle is 0.8 degree or less because the maximum rotating rate of the steering wheel may be 2000 degrees/sec. This detection accuracy is much higher than the required detection accuracy for a product, or 1.5 degrees; in other words, abnormalities can be detected with high accuracy.
According to a further aspect of the present invention, in the rotational angle detector, it is desirable to judge the count (number of times when the angle detection signal is beyond the allowable maximum value) as being beyond the preset number when two out of three consecutive counts are found beyond the preset number.
With this arrangement, the controlled system can be controlled in response only to an abnormality signal to be addressed, which arises from an abnormal operation, without responding to external noise or any other abnormal signal which need not be addressed, so that the controlled system can be controlled efficiently and smoothly.
According to a further aspect of the present invention, in the rotational angle detector, it is desirable to judge the count (number of times when the angle detection signal is beyond the allowable maximum value) as being beyond the preset number when six out of 64 consecutive counts are found beyond the preset number.
With this arrangement, the probability of avoiding unnecessary control over abnormal signals caused by mere momentary external noise is increased and sporadic permanent abnormalities can be detected so that the controlled system can be controlled with more safety.
Furthermore, according to a further aspect of the present invention, the rotational angle detector comprises: a rotational angle detecting section which detects an angle detection signal correspondent to a rotational state of a rotor and feeds the angle detection signal to a control section; the control section which calculates the angle detection signal fed from the rotational angle detecting section to generate an angle set signal and sends the generated angle set signal through a controller to a controlled system; and a memory which stores an allowable maximum setting, wherein the control section has means to concurrently perform a first calculation step and a second calculation step for the angle detection signal fed from the rotational angle detecting section to generate a first angle set signal and a second angle set signal, calculate the difference between the first angle set signal and second angle set signal, compare the calculated difference with the allowable maximum setting, and if the calculated difference is judged as being above the allowable maximum setting, output an abnormality signal instead of the angle set signal.
In the above means, the memory stores the allowable maximum setting and the control section concurrently performs a first calculation step and a second calculation step for the angle detection signals fed from the rotational angle detecting section to generate a first angle set signal and a second angle set signal, calculates the difference between the first angle set signal and second angle set signal, compares the calculated difference with the allowable maximum setting read from the memory, and the calculated difference is judged as being below the allowable maximum setting, generates and outputs a given angle set signal at the time of angle set signal output, while if the calculated difference is judged as being above the allowable maximum setting, generates and outputs an abnormality signal in addition to a given angle set signal at the time of angle set signal output. Therefore, thanks to output of the abnormality signal, the user of the rotational angle detector can not only immediately be notified of the presence of an abnormality in the operation of the rotational angle detector but also avert the risk of the controlled system being improperly controlled due to the feed of an incorrect angle set signal.
According to a further aspect of the present invention, in the rotational angle detector, it is desirable for the control section to perform the first calculation step and the second calculation step using different lookup tables.
With this arrangement, if either of the lookup table for the first step and the lookup table for the second step contains some fault, the result of comparison made in an output decision section will be different from the normal result whenever that fault is picked up, which makes it possible to identify the presence of a fault with more reliability.
According to a further aspect of the present invention, in the rotational angle detector, it is desirable for the control section to perform the first calculation step and the second calculation step using different algorithms.
With this arrangement, if either of the algorithm for the first step and the algorithm for the second step contains some fault, the result of comparison made in the output decision section will be different from the normal result whenever that fault is picked up, which makes it possible to identify the presence of a fault with more reliability. Also, the algorithms"" portions with low abnormality detection accuracy are mutually complementary so that the abnormality detection capability can be improved.
According to a further aspect of the present invention, in the rotational angle detector, it is desirable for the control section to detect an angle detection signal in a short cycle and output the angle set signal in a cycle longer than the detection cycle for angle detection signals.
With this arrangement, an abnormal operation can be detected before the rotational angle detection signal output cycle, and the abnormality signal concerned is outputted in combination with an angle set signal selected from the memory as appropriate, thereby preventing the controlled system from being controlled improperly.
According to a further aspect of the present invention, in the rotational angle detector, it is desirable that the first calculation step and the second calculation step be performed by different control sections.
With this arrangement, if either of the calculating operation for the first step and the calculating operation for the second step contains some fault, it is possible to avert the risk of failing to output an abnormality signal which might arise if two calculating operations having the same kind of fault should output the same result and produce no result difference; therefore the probability of picking up faults is increased and faults can be detected with more reliability.